3rd generation partnership project (3GPP) long term evolution (LTE) evolved from a universal mobile telecommunications system (UMTS) is introduced as the 3GPP release 8. The 3GPP LTE uses orthogonal frequency division multiple access (OFDMA) in a downlink, and uses single carrier-frequency division multiple access (SC-FDMA) in an uplink. The 3GPP LTE employs multiple input multiple output (MIMO) having up to four antennas.
In a hybrid automatic repeat request (HARQ) scheme, whether data received by a physical layer has an unrecoverable error is determined and retransmission is requested upon detecting the error, thereby improving performance.
If no error is detected from the received data, a receiver transmits a positive-acknowledgement (ACK) signal as a reception acknowledgment so that a transmitter is informed that the data is successfully received. Otherwise, if an error is detected from the received data, the receiver transmits a negative-acknowledgement (NACK) signal as a reception acknowledgment so that the transmitter is informed that the error is detected. When the NACK signal is received, the transmitter can retransmit data.
In recent years, there is an ongoing discussion on 3GPP LTE-advanced (LTE-A) evolved from the 3GPP LTE. The 3GPP LTE-A ensures backward compatibility with the 3GPP LTE, and supports a wideband by using carrier aggregation.
The 3GPP LTE-A has a basic frequency band supporting compatibility with the 3GPP LTE and an extended frequency band not supporting compatibility with the 3GPP LTE.
A physical channel used in the 3GPP LTE does not consider an extended frequency band supported by the 3GPP LTE-A. Therefore, a reception acknowledgment for HARQ may not be transmitted through the physical channel when data is transmitted in the extended frequency band.